First, let me say that I understand your concerns, and appreciate your desire for privacy.
The nudge feature is not intended to be any form of invasion of privacy. The only information that it provides to the person using it -- the lack of the other person's recent updates and the mutual friend status between the two -- is information that is publicly available on the other person's userinfo page. The email address is not released for the nudge process; also, it is only possible to nudge someone who is a mutual friend, and it is not possible to nudge someone just based on email address.
The primary purpose of the nudge feature is to remind someone that they have a LiveJournal account and that someone would want to read their updates. It isn't intended as a way of inquiring why someone hasn't been updating, and there is no obligation involved with the nudge.
LiveJournal administrators are aware of some of the concerns that people have with the nudge feature. There will at some point in the future be a way to "opt out" of nudging, so that people who do not wish to be nudged in this way can disable it. This opt-out will be provided as soon as possible, though there is no way to know when that will be.
Also, please note that the nudge feature judges activity only by the last time the person wrote an entry in their journal. Commenting on another journal does not make someone "active" from the nudge feature's perspective. Even if someone commented recently in your journal, if they haven't updated in over a week, they will be eligible to be nudged by any mutual friend.
The reply I've posted:
I realise that this only applies to friends, but friends may not always realise the problems they can cause by using this feature.
One of the points I was trying to make is that by doing this you are sending an email to someone who may have concealed their email address on Livejournal, or may have put a different contact address on their personal info page, rather than the one they used to join Livejournal. You may be causing big problems for them by revealing the existence of a journal to a third party.
Why have "opt in" as the default, since it's something that vulnerable users probably won't realise can cause problems for them until it's too late?
Later Added another comment:
Also, why have a week as the period after which you can nudge someone? It's a ridiculously short time if someone is travelling or ill, or simply doesn't feel the need to post very often.
Anyone else wanting to comment, it's http://www.livejournal.com/support/see_request.bml?id=541646&